1. Field of the Invention
The invention relates to a monitoring device for signal echo sensors, preferably for measuring spacing between motor vehicles using ultrasonic pulses, and, more particularly, to a monitoring device for signal echo sensors that includes at least one transmitting unit for broadcasting a signal and at least one receiving unit for receiving a reflected or echo signal, reflected by an object, of the broadcast signal and a control and evaluation unit for generating the broadcast signal and evaluating the reflected or echo signal.
2. Prior Art
Various kinds of monitoring devices used as spacing sensors are known, based on various physical sensor principles, such as ultrasound, infrared, or microwaves. For instance, spacing sensors are known in which a pulse-type signal is transmitted by an evaluation unit, and the time is measured until the reception of an echo signal. Only after that is a new transmission pulse sent. A disadvantage proves to be the vulnerability of the system to identical kinds of signals received. For instance if ultrasound is used, if other vehicles located in the vicinity are also equipped with ultrasound monitoring devices, then misinterpretations or incorrect reports can result. If a different vehicle has the same pulse train frequency, for instance, then incorrect measurements can be made without being noticed, since the ultrasound monitoring device assumes that an echo signal is being received.
Furthermore, the known ultrasound sensors, which always use the same pulse train frequency, are only limitedly usable when there are multiple obstacles, since interfering multiple echoes are often interpreted incorrectly. In the case of multiple echoes, additional waiting times are also needed before a new transmission pulse can be sent. Even without such problems, at least the waiting time required by a signal to travel a maximum distance back and forth must be observed.
From German Patent Disclosure DE 40 23 538 A1, a collision warning device is also known, which by employing two sensors and so-called crosswise measurement can distinguish between walls, corners and edges. A disadvantage here is that the two sensors must be operated sequentially, making the system relatively slow. If the object moves between the measurements of the two sensors, this can lead to misinterpretations.
The object of the invention is to create an ultrasound monitoring device which by suppressing interference from ultrasound spacing sensors makes fast followup objects, even of moving objects possible.
This object, and others which will be made more apparent hereinafter, are attained in a monitoring device for signal echo sensors that includes at least one transmitting unit for broadcasting a transmitted signal and at least one receiving unit for receiving a reflected or echo signal, reflected by an object, of the transmitted signal and a control and evaluation unit for generating the broadcast signal and evaluating the reflected or echo signal.
According to the invention the at least one transmitting unit monitoring device generates the transmitted signal with a characteristic signal shape and the control and evaluation unit has an adaptive filter integrated therein for evaluating the echo signal jointly with the transmitted signal.
The preferably ultrasonic monitoring device according to the invention provides rapid detection of objects, even moving objects, by transmitting a characteristic signal shape, such as a random signal or a stochastic pulse train, which together with an echo signal is evaluated via an adaptive filter, integrated with an evaluation unit, for determining the spacing of an object from the transmitting unit. As a result, automatic suppression of any interference is also possible by use of the adaptive filter. Simultaneous operation of a plurality of sensors without mutual interference also proves to be advantageous, by using different random signals as transmission signals in conjunction with an adaptive filter. This adaptive filter can advantageously be embodied as a digital filter. Preferably, the filter is a so-called FIR (Finite Impulse Response) filter, which functions in nonrecursive fashion.
Advantageous features of the invention will become apparent from the characteristics recited in the dependent claims.